Reproduction in the Macropod Marsupial Potorous tridactylus (Kerr).

Thirty-five female Tasmanian rat-kangaroos, Potorous tridmtylus (Kerr), were studied. This marsupial is both polyoestrous and monovular. The length of the oestrous cycle is approximately 42 days (range 39-44 days). Study of vaginal smears over intervals that included 14 oestrous periods revealed that the proportions of cornified cells reached a maximum of over 80% at oestrus, and conversely the other cell types (i.e. nucleated epithelial cells and polymorphonuclear leucocytes) were at minimal concentrations. In four females copulation was apparently permitted at any time during the period of rapid increase in the proportion of cornified cells. One female repeatedly received a male over a 12-day heat period. Copulations were brief and were observed only between 4.00 p.m. and 1.45 a.m. In two females coitus was found to precede ovulation. The gestation period (defined as the interval between copulation and parturition) varied between 30 and 43 days in four animals. In one instance parturition was witnessed 37.5 days after copulations that were restricted to a 12-hr period. A marked increase in pouch vascularity occurred a few hours prior to parturition. Parturition was witnessed on one occasion and is described. The time taken to reach the pouch was 10 min; attachment was made in a further 12 min. On another occasion a neonatus removed from a teat shortly after parturition took 5 min to locate the teat and a further 15 min to complete reattachment. Permanent attachment of the offspring to a teat occupied 64 days in one instanc; in another it lasted 46 days but as the offspring died 6 days later it may be that the teat was vacated prematurely. The manner in which permanent nipple attachment is achieved is discussed and a description of the development of external features of pouch young is given. Nipples increased in both length and diameter during the first 115 days of suckling, after which regresslon began. The regresslon was correlated wlth the process of weanlng. An indication of three successive lactations was obtained from nipple dimensions. Pregnancy (occupying about 38 days) did not prevent oestrus from appearing at the normal time (i.e. approximately 42 days after the preceding oestrus). Mating occurred at the post-partum oestrus but lactation inhibited further oestrous cycles as well as delaying the development of the resultant uterine embryo. The period of delayed pregnancy can be as long as 4+ months. During most of this period the embryo remained free in the uterus as a dormant blastocyst, diameter 0.25-0.28 mm. Embryonic development was resumed during the weaning period when suckling was intermittent and diminishing or when the offspring was prematurely lost. Observations on both captive and wild populations suggested the existence of two breeding seasons, one in late winter and early spring, the other in summer. However, the evidence on which these breeding seasons are based is extremely limited. Reproduction in Potorous is compared with that in other marsupial species.